Re: responses to pterosaur discussion

[Ronald Orenstein <ornstn@home.com>]

At 11:54 AM 07/02/01 -0600, Demetrios M. Vital wrote:
> So if we
> cannot establish certain differences between groups, such as the
> hemoglobin efficiency, then all we have left to compare is the gross
> physical structure.  And if guesses are the best we can deal with,
> why shouldn't we deal with those educated
> guesses?

Because they may not be educated.  Listen, speculation is dandy, but
if you are proposing a serious hypothesis it can't be built on a pile of
"ifs".  In this case, the margin for error you would get
in comparing respiratory efficiency between birds and pterosaurs without
physiological information may well be so great that you could never
clearly answer even the simple question as to whether their respiratory
efficiencies were alike or different.  Can you tell me, for example,
the tidal volume in pterosaur lungs?  The degree of
vascularization?  The oxygen-binding ability of pterosaur
hemoglobin?

We are finding in living turtles that there are many different
hemoglobins with different oxygen-binding abilities, and an individual
species may have as many as six.  Thus the range of physiological
variation has the potential to be far greater than the physical structure
of a turtle skeleton could possibly indicate.  The same may well be
true for other taxa.

Besides, it is one thing to speculate on how pterosaurs breathed (and a
perfectly valid thing too, especially if you could figure out a way to
test your hypothesis).  It is another thing to get into a second
level of speculation in which you propose to explain pterosaur extinction
by a physiological mechanism you cannot prove existed.  This is
piling speculation on speculation.  It may be fun, but it is hardly
useful science.

> Yes, it
> would take an in-depth study to guage the exact differences between taxa,
> but would you go into a study or discussion assuming all taxa have the
> same respiratory abilities?

Of course not - precisely my point.  But would you go into a study
assuming that the physiological aspects of respiration, which you cannot
measure in pterosaurs (or in Mesozoic birds, for that matter), were so
much alike in birds and pterosaurs that a difference in physical
respiratory structure would translate directly into a difference in
respiratory efficiency?

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                
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